Proposed Changes to the Format of the IANA IPv6 Registry
A cleaner way to organize and display the official list of IPv6 addresses.
Huston, G., "Proposed Changes to the Format of the IANA IPv6 Registry", RFC 4147, DOI 10.17487/RFC4147, August 2005, <https://www.rfc-editor.org/info/rfc4147>.
@misc{rfc4147,
series = {Request for Comments},
number = 4147,
howpublished = {RFC 4147},
publisher = {RFC Editor},
doi = {10.17487/RFC4147},
url = {https://www.rfc-editor.org/info/rfc4147},
author = {G. Huston},
title = {{Proposed Changes to the Format of the IANA IPv6 Registry}},
pagetotal = 10,
year = 2005,
month = aug,
} RFC text
Contents
Network Working Group G. Huston
Request for Comments: 4147 APNIC
Category: Informational August 2005
Proposed Changes to the Format of the IANA IPv6 Registry
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document proposes a revised format for the IANA IPv6 address
registries. Rather than providing a formal definition of the format,
it is described by giving examples of the (current as of preparation
of this document) contents of the registries in the proposed format.
The proposed format would bring the IANA IPv6 address registries into
alignment with the current IPv6 Address Architecture specification,
as well as update it to a more useful and generally accepted format.
1. Introduction
This document proposes a revised format for the IANA IPv6 address
registries. The proposed format would bring the IANA IPv6 address
registries into alignment with the current IPv6 Address Architecture
specification, as well as update it to a more useful and generally
accepted format.
The current (as of preparation of this document) IANA IPv6 registries
[iana-ipv6-registry] [iana-ipv6-tla] are based on a now-deprecated
address architecture that used the concept of Top Level Aggregation
Identifiers (TLAs) and sub-TLAs. The current IPv6 Address
Architecture [RFC3513] uses the terminology of Global Identifiers
instead of TLAs and sub-TLAs.
2. IPv6 Address Registry
The proposed format for the IPv6 address registry is indicated by
example, using the registry state that is current as of preparation
of this document, in Figure 1. The registry explicitly notes which
entity is placing a reservation on an address block and notes the
defining RFC document for each allocation.
The proposed format of the registry is a title line, the date of the
last change to the registry, the registry in a tabular format, notes
and references.
The table uses 4 columns. Within the table, the first column
contains an IPv6 address prefix, using a hexadecimal notation of the
address prefix and a prefix length. There are no overlapping address
blocks in the first column, and the set of address blocks in the
registry spans the entire IPv6 address space. The second column
denotes the current disposition of the address block, using notation
derived from the defining RFC document. The third column contains a
reference to the RFC that describes the current disposition of the
address block. The fourth column uses numeric footnote notation to
reference any additional text associated with the address block.
The notes in the registry may include a summary of previous
disposition status values associated with an address block, as this
summary is specifically not included in the registry table. The
notes are numbered sequentially.
The reference section uses a conventional citation format. The
references include documents referenced in the registry table and
documents referenced in the notes.
-----------------------------------------------------
INTERNET PROTOCOL VERSION 6 ADDRESS SPACE
[last updated 13 January 2005]
IPv6 Prefix Allocation Reference Note
----------- ---------- --------- ----
0000::/8 Reserved by IETF RFC3513 [1]
0100::/8 Reserved by IETF RFC3513
0200::/7 Reserved by IETF RFC4048 [2]
0400::/6 Reserved by IETF RFC3513
0800::/5 Reserved by IETF RFC3513
1000::/4 Reserved by IETF RFC3513
2000::/3 Global Unicast RFC3513 [3]
4000::/3 Reserved by IETF RFC3513
6000::/3 Reserved by IETF RFC3513
8000::/3 Reserved by IETF RFC3513
A000::/3 Reserved by IETF RFC3513
C000::/3 Reserved by IETF RFC3513
E000::/4 Reserved by IETF RFC3513
F000::/5 Reserved by IETF RFC3513
F800::/6 Reserved by IETF RFC3513
FA00::/7 Reserved by IETF RFC3513
FC00::/7 Reserved by IETF RFC3513
FE00::/9 Reserved by IETF RFC3513
FE80::/10 Link Local Unicast RFC3513
FEC0::/10 Reserved by IETF RFC3879 [4]
FF00::/8 Multicast RFC3513
Notes:
[0] The IPv6 address management function was formally delegated to
IANA in December 1995 [RFC1881].
[1] The "unspecified address", the "loopback address", and the
IPv6 Addresses with Embedded IPv4 Addresses are assigned out
of the 0000::/8 address block.
[2] 0200::/7 was previously defined as an OSI NSAP-mapped prefix
set [RFC1888]. This definition has been deprecated as of
December 2004 [RFC4048].
[3] The IPv6 Unicast space encompasses the entire IPv6 address
range with the exception of FF00::/8. [RFC3513] IANA unicast
address assignments are currently limited to the IPv6 unicast
address range of 2000::/3. IANA assignments from this block
are registered in the IANA registry: iana-ipv6-unicast-
address-assignments.
[4] FEC0::/10 was previously defined as a Site-Local scoped
address prefix. This definition has been deprecated as of
September 2004 [RFC3879].
References:
[RFC1881] The IAB and IESG, "IPv6 Address Allocation Management",
RFC 1881, December 1995.
[RFC1888] J. Bound et al, "OSI NSAPs and IPv6", RFC 1888, August
1996.
[RFC3513] R. Hinden and S. Deering, "IP Version 6 Addressing
Architecture", RFC 3513, April 2003.
[RFC3879] C. Huitema and B. Carpenter, "Deprecating Site Local
Addresses", RFC 3879, September 2004.
[RFC4048] B. Carpenter, "RFC 1888 Is Obsolete", RFC 4048, April
2005.
-----------------------------------------------------
Figure 1
2.1. Notes on Proposed Format Changes to the Registry
o The textual preamble at the start of the registry has been
removed, in deference to the use of standard IPv6 prefix notation
in the registry.
o Binary prefix notation has been replaced by standard IPv6 prefix
hexadecimal notation, and the fraction of address space column has
been replaced with the reference to the relevant RFC that defines
the disposition of the address block. Footnote references are
also displayed in a consistent fashion.
o The terminology "Unassigned" has been replaced by the more precise
phrase "Reserved by IETF", indicating the body that has the token
to permit reassignment of the status of this address block.
o The "Formerly Site-Local" entry in the body of the registry has
been replaced with an explicit reference to deprecation. A
similar treatment is proposed for 0200::/8, although the RFC
number for the deprecation document has yet to be assigned. There
is a distinction drawn between the current status of a registry
and the set of registry actions that have lead to the current
state. The registry table describes the current status of the
registry, while the text footnotes are used to describe the set of
transactions leading to the current state, including any former
states.
o Annotations that are references to footnotes are included in the
registry in a separate column.
o The text commentary on unicast, multicast and anycast addresses
has been removed, as there is no distinction between anycast and
unicast addresses and multicast addresses are explicitly flagged
in the registry.
o A note and a corresponding reference to RFC1881 was added to
record the formal delegation of the IPv6 address management
function to IANA.
3. Global Unicast IPv6 Address Registry
The proposed registry format for Global Unicast IPv6 address block
allocations is indicated by example, using the registry state that
was current as of preparation of this document, in Figure 2. The
registry notes the current allocations, and does not include any
notation of intended future allocations or reservations. All address
space not listed in this registry forms the IANA unallocated address
pool, to be allocated by IANA as per the prevailing address
allocation policies.
The proposed format of the registry is a title line, the date of the
last change to the registry, the registry in a tabular format, notes
and references.
The table uses 4 columns. Within the table, the first column is an
IPv6 address prefix, using a hexadecimal notation of the address
prefix and a prefix length. There are no overlapping address blocks
in the first column. The entries here describe only IANA allocations
of address blocks. Temporary IANA reservations for future
allocations, allocation expansion windows and any other internal IANA
states are not described in this registry. The second column
describes the current disposition of the address block, by noting
either the Regional Internet Registry (RIR) to whom the address block
was assigned, or the intended use of the address block. The third
column is the date of the IANA allocation, including the day of the
month. The fourth column uses numeric footnote notation to reference
any additional text associated with the address block.
The notes in the registry may include a summary of previous
disposition status values associated with an address block, as this
summary is specifically not included in the registry table. The
notes are numbered sequentially.
The reference section uses a conventional citation format. The
references include documents referenced in the registry table and
documents referenced in the notes.
-----------------------------------------------------
IPV6 GLOBAL UNICAST ADDRESS ASSIGNMENTS
[last updated 13 January 2005]
Global Unicast Prefix Assignment Date Note
--------------------- ---------- ------ ----
2001:0000::/23 IANA 01 Jul 99 [1]
2001:0200::/23 APNIC 01 Jul 99
2001:0400::/23 ARIN 01 Jul 99
2001:0600::/23 RIPE NCC 01 Jul 99
2001:0800::/23 RIPE NCC 01 May 02
2001:0A00::/23 RIPE NCC 02 Nov 02
2001:0C00::/23 APNIC 01 May 02 [2]
2001:0E00::/23 APNIC 01 Jan 03
2001:1200::/23 LACNIC 01 Nov 02
2001:1400::/23 RIPE NCC 01 Feb 03
2001:1600::/23 RIPE NCC 01 Jul 03
2001:1800::/23 ARIN 01 Apr 03
2001:1A00::/23 RIPE NCC 01 Jan 04
2001:1C00::/22 RIPE NCC 01 May 04
2001:2000::/20 RIPE NCC 01 May 04
2001:3000::/21 RIPE NCC 01 May 04
2001:3800::/22 RIPE NCC 01 May 04
2001:4000::/23 RIPE NCC 11 Jun 04
2001:4200::/23 ARIN 01 Jun 04
2001:4400::/23 APNIC 11 Jun 04
2001:4600::/23 RIPE NCC 17 Aug 04
2001:4800::/23 ARIN 24 Aug 04
2001:4A00::/23 RIPE NCC 15 Oct 04
2001:4C00::/23 RIPE NCC 17 Dec 04
2001:5000::/20 RIPE NCC 10 Sep 04
2001:8000::/19 APNIC 30 Nov 04
2001:A000::/20 APNIC 30 Nov 04
2002::/16 6to4 01 Feb 01 [3]
2003:0000::/18 RIPE NCC 12 Jan 05
3FFE::/16 6BONE 01 Dec 98 [4]
Notes:
[0] The assignable Global Unicast Address space is defined
in [RFC3513] as being the address block defined by the
prefix 2000::/3. All address space in this block not
listed in the table above is reserved by IANA for
future allocation.
[1] The prefix assigned to the IANA, 2001:0000::/23, is for
assignment for testing, experimental and trial usage by IANA
[RFC2928].
[2] 2001:0DB8::/32 has been assigned as a NON-ROUTABLE
range to be used for documentation purposes [RFC3849].
[3] 2002::/16 is reserved for use in 6to4 deployments [RFC3056]
[4] 3FFE::/16 is an experimental allocation to the 6BONE
[RFC2471]. This prefix will be returned to the unassigned
address pool on the 6th June 2006 [RFC3701].
References:
[RFC2471] R. Hinden, R. Fink and J. Postel, "IPv6 Testing
Address Allocation", RFC 2471, December 1998.
[RFC2928] R. Hinden, S. Deering, R. Fink and T. Hain,
"Initial IPv6 Sub-TLA ID Assignments", RFC 2928,
September 2000.
[RFC3056] B. Carpenter and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC3513] R. Hinden and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003.
[RFC3701] R. Fink and R. Hinden, "6bone (IPv6 Testing Address
Allocation) Phaseout", RFC 3701, March 2004.
[RFC3849] G. Huston, A. Lord, A and P. Smith, "IPv6 Address
Prefix Reserved for Documentation", RFC 3849, July
2004.
-----------------------------------------------------
Figure 2
3.1. Notes on Proposed Format Changes to the Registry
o The current registry name "iana-ipv6-tla-assignments" should be
changed to "iana-ipv6-unicast-address-assignments".
o The title of the registry has been altered to remove the reference
to "TOP LEVEL AGGREGATION IDENTIFIER".
o The TLA and Sub-TLA identifier assignments have been rolled into a
single set of address prefixes and their assignment.
o The text commentary at the start of the registry contents has been
removed.
o Binary value notation of the address prefixes has been removed.
o Further commentary on assignments, such as the planned phaseout of
the 6BONE, is placed in a footnote.
o The registry continuation lines using ellipsis notation have been
removed.
o Only assigned addresses are listed. All unassigned addresses,
marked in the original IANA registry with the assignment note of
"(future assignment)" have been removed, as has the entry marked
"reserved *)".
o Address assignments are listed using prefix size notation of the
actual allocation, rather than reporting the allocation in sub-
units of /23 prefixes.
o The date of the IANA action includes the day of the month as well
as the month and year.
4. IANA Considerations
IANA is advised to adopt these formats for the IPv6 address registry
and the IPv6 Global Unicast address registry.
5. Security Considerations
Security of the Internet's routing system relies on the ability to
authenticate an assertion of unique control of an address block.
Measures to authenticate such assertions rely on validation that the
address block forms part of an existing allocated address block, and
that there is a trustable reference from the IANA address registry to
the RIR, and a trustable reference from the RIR's registry to a Local
Internet Registry or end-user Internet Service Provider.
The proposed format for the IANA registry is a small step towards the
creation of a registry that can be used as a trust point for
commencing a chain of address validation. Consideration should be
given to IANA registry publication formats that are machine
parseable, and also the use of file signatures and associated
certificate mechanisms to allow applications to confirm that the
registry contents are current, and that they have been published by
the IANA.
6. Acknowledgements
This document was prepared with the assistance of Kurt Lindqvist,
Thomas Narten, Paul Wilson, David Kessens, Bob Hinden and Brian
Haberman. Pekka Savola, Brian Carpenter, Christian Huitema and
Michael Patton provided helpful review comments.
7. References
7.1. Normative References
[RFC3513] Hinden, R. and S. Deering, "Internet Protocol
Version 6 (IPv6) Addressing Architecture",
RFC 3513, April 2003.
7.2. Informative References
[iana-ipv6-registry] IANA, "IANA IPv6 Address Registry",
December 2004.
[iana-ipv6-tla] IANA, "IANA Registry of IPv6 Top Level
Aggregation Identifier Assignments",
December 2004.
Author's Address
Geoff Huston
Asia Pacific Network Information Centre
EMail: gih@apnic.net
URI: http://www.apnic.net
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AI ELI5
On this page
§1Introduction and Problem
RFC 4147 identifies a problem with how IANA organized its official IPv6 address registries. The registries used outdated terminology from an earlier IPv6 address architecture: Top Level Aggregation Identifiers (TLAs) and sub-TLAs. By the time this RFC was written, the current IPv6 standard, RFC 3513, had moved away from this terminology and now uses Global Identifiers instead. The registries were out of step with the standard they were supposed to document.
The address book was organized using old-fashioned categories. A newer, better system had already been adopted, but the book had not been updated to match.
§2The Proposed Registry Format
The RFC proposes a new format for the two main IPv6 registries: the overall IANA IPv6 Address Space registry and the Global Unicast IPv6 Address Assignments registry.
The new format uses a simple tabular layout with four columns: the IPv6 address prefix (in standard hexadecimal notation with prefix length, like 2001:0000::/23), the allocation status or receiving entity (such as Global Unicast or the name of a Regional Internet Registry), a reference to the RFC document that defines or justifies the allocation, and footnote numbers for additional context. The entire address space is covered in non-overlapping blocks, and unassigned space is noted as Reserved by IETF.
For example, the block 2000::/3 is allocated for Global Unicast addresses and is defined by RFC 3513. Special-use ranges like FE80::/10 (link-local) and FF00::/8 (multicast) are clearly marked with their purposes and RFCs.
Instead of using confusing old terms, each address block now lists: what the block is, who it is for or what it does, which RFC explains it, and any extra notes. The format is clean and easy to scan.
§3Key Changes and Design Choices
Several specific improvements are made over the old format:
Terminology: The phrase Reserved by IETF replaces vague words like Unassigned, making it clear that the IETF controls whether these blocks can be reassigned in the future.
Notation: Binary notation is replaced by standard hexadecimal IPv6 prefix notation (e.g., 2001:0000::/23 instead of binary digits), which is what networking tools and operators use every day. The column showing a fraction of address space is removed and replaced with direct RFC references.
History: When an address block has changed status over time (such as the Site-Local addresses in FEC0::/10, which were deprecated by RFC 3879), the registry notes explain the history in footnotes rather than cluttering the main table. This keeps the current state clear while preserving historical context.
Completeness: Each registry table now explicitly covers the entire IPv6 address space, making it obvious what is allocated, reserved, or available for future allocation.
The new format drops confusing terms, uses the notation that engineers actually type, explains why each block is important by citing the RFC, and keeps historical notes separate from the current facts.
§4Registry Examples
The RFC includes two detailed example tables showing the proposed format with real address allocations as they stood in 2005.
The main IPv6 address space registry spans from 0000::/8 (reserved) through FF00::/8 (multicast). Key allocations include 2000::/3 for global unicast (the main pool for public internet addresses), various blocks reserved for future use, link-local and multicast ranges, and experimental blocks like 3FFE::/16 (6BONE, noted as returning to the unassigned pool in 2006).
The global unicast assignments registry shows how IANA has distributed 2000::/3 space to regional registries and for special purposes. The table lists each /23 or larger block assigned to APNIC, ARIN, RIPE NCC, LACNIC, to 6to4 (2002::/16), and to documentation purposes (2001:0DB8::/32, now familiar as the example prefix in RFC 3849).
The RFC shows what the new registries would look like, with real examples of which blocks are for everyday internet use, which are reserved, and which are for special purposes like testing or historical experiments.
§5Security and Trust
The RFC notes that the security of the internet routing system depends on being able to verify that an organization genuinely controls the IPv6 addresses it claims. This verification starts with trusting the IANA registry: if you see an address block assigned to a Regional Internet Registry in the IANA registry, you can then check that RIR's registry to confirm the assignment to an actual ISP or organization.
A clearer, more standardized registry format helps this chain of trust. The RFC suggests that IANA registries should be machine-parseable (not just human-readable tables) and potentially signed with digital certificates so applications can confirm they are reading current, official data straight from IANA.
When someone says they own an IPv6 address, networks check the IANA list to verify. A clearer list helps this work better, and digital signatures could make it even more trustworthy.